VHP Photo Glossary: block

Photograph by C. Heliker on
January 26, 1988

Block

A volcanic block is a solid rock fragment greater than 64 mm in diameter
that was ejected from a volcano during an explosive eruption. Blocks
commonly consist of solidified pieces of old lava flows that were
part of a volcano's cone.

This block was ejected into the air by an explosion caused by
the collapse of an active lava delta
at Kilauea Volcano, Hawai`i. New land built by lava often slides
into the ocean, which enables seawater to mix with lava
and hot rocks. Such violent mixing may trigger steam explosions that can
blast hot rocks 10 to 50 cm in diameter more than 50 m inland.